You can just allocate a portion of a shared memory segment, copy the message
to that buffer, send the offset of that portion of shared memory to another
process, and you are done. Let's see the example:

#include<boost/interprocess/managed_shared_memory.hpp>#include<cstdlib>//std::system
#include<sstream>intmain(intargc,char*argv[]){usingnamespaceboost::interprocess;if(argc==1){//Parent process
//Remove shared memory on construction and destruction
structshm_remove{shm_remove(){shared_memory_object::remove("MySharedMemory");}~shm_remove(){shared_memory_object::remove("MySharedMemory");}}remover;//Create a managed shared memory segment
managed_shared_memorysegment(create_only,"MySharedMemory",65536);//Allocate a portion of the segment (raw memory)
std::size_tfree_memory=segment.get_free_memory();void*shptr=segment.allocate(1024/*bytes to allocate*/);//Check invariant
if(free_memory<=segment.get_free_memory())return1;//An handle from the base address can identify any byte of the shared
//memory segment even if it is mapped in different base addresses
managed_shared_memory::handle_thandle=segment.get_handle_from_address(shptr);std::stringstreams;s<<argv[0]<<" "<<handle;s<<std::ends;//Launch child process
if(0!=std::system(s.str().c_str()))return1;//Check memory has been freed
if(free_memory!=segment.get_free_memory())return1;}else{//Open managed segment
managed_shared_memorysegment(open_only,"MySharedMemory");//An handle from the base address can identify any byte of the shared
//memory segment even if it is mapped in different base addresses
managed_shared_memory::handle_thandle=0;//Obtain handle value
std::stringstreams;s<<argv[1];s>>handle;//Get buffer local address from handle
void*msg=segment.get_address_from_handle(handle);//Deallocate previously allocated memory
segment.deallocate(msg);}return0;}

You want to create objects in a shared memory segment, giving a string name
to them so that any other process can find, use and delete them from the
segment when the objects are not needed anymore. Example:

#include<boost/interprocess/managed_shared_memory.hpp>#include<cstdlib>//std::system
#include<cstddef>#include<cassert>#include<utility>intmain(intargc,char*argv[]){usingnamespaceboost::interprocess;typedefstd::pair<double,int>MyType;if(argc==1){//Parent process
//Remove shared memory on construction and destruction
structshm_remove{shm_remove(){shared_memory_object::remove("MySharedMemory");}~shm_remove(){shared_memory_object::remove("MySharedMemory");}}remover;//Construct managed shared memory
managed_shared_memorysegment(create_only,"MySharedMemory",65536);//Create an object of MyType initialized to {0.0, 0}
MyType*instance=segment.construct<MyType>("MyType instance")//name of the object
(0.0,0);//ctor first argument
//Create an array of 10 elements of MyType initialized to {0.0, 0}
MyType*array=segment.construct<MyType>("MyType array")//name of the object
[10]//number of elements
(0.0,0);//Same two ctor arguments for all objects
//Create an array of 3 elements of MyType initializing each one
//to a different value {0.0, 0}, {1.0, 1}, {2.0, 2}...
floatfloat_initializer[3]={0.0,1.0,2.0};intint_initializer[3]={0,1,2};MyType*array_it=segment.construct_it<MyType>("MyType array from it")//name of the object
[3]//number of elements
(&float_initializer[0]//Iterator for the 1st ctor argument
,&int_initializer[0]);//Iterator for the 2nd ctor argument
//Launch child process
std::strings(argv[0]);s+=" child ";if(0!=std::system(s.c_str()))return1;//Check child has destroyed all objects
if(segment.find<MyType>("MyType array").first||segment.find<MyType>("MyType instance").first||segment.find<MyType>("MyType array from it").first)return1;}else{//Open managed shared memory
managed_shared_memorysegment(open_only,"MySharedMemory");std::pair<MyType*,std::size_t>res;//Find the array
res=segment.find<MyType>("MyType array");//Length should be 10
if(res.second!=10)return1;//Find the object
res=segment.find<MyType>("MyType instance");//Length should be 1
if(res.second!=1)return1;//Find the array constructed from iterators
res=segment.find<MyType>("MyType array from it");//Length should be 3
if(res.second!=3)return1;//We're done, delete all the objects
segment.destroy<MyType>("MyType array");segment.destroy<MyType>("MyType instance");segment.destroy<MyType>("MyType array from it");}return0;}

Boost.Interprocess offers offset_ptr smart
pointer family as an offset pointer that stores the distance between the
address of the offset pointer itself and the address of the pointed object.
When offset_ptr is placed in a shared memory segment, it can point safely
objects stored in the same shared memory segment, even if the segment is
mapped in different base addresses in different processes.

This allows placing objects with pointer members in shared memory. For example,
if we want to create a linked list in shared memory:

Boost.Interprocess allows creating complex
objects in shared memory and memory mapped files. For example, we can construct
STL-like containers in shared memory. To do this, we just need to create
a special (managed) shared memory segment, declare a Boost.Interprocess
allocator and construct the vector in shared memory just if it was any other
object.

#include<boost/interprocess/managed_shared_memory.hpp>#include<boost/interprocess/containers/vector.hpp>#include<boost/interprocess/allocators/allocator.hpp>#include<string>#include<cstdlib>//std::system
usingnamespaceboost::interprocess;//Define an STL compatible allocator of ints that allocates from the managed_shared_memory.
//This allocator will allow placing containers in the segment
typedefallocator<int,managed_shared_memory::segment_manager>ShmemAllocator;//Alias a vector that uses the previous STL-like allocator so that allocates
//its values from the segment
typedefvector<int,ShmemAllocator>MyVector;//Main function. For parent process argc == 1, for child process argc == 2
intmain(intargc,char*argv[]){if(argc==1){//Parent process
//Remove shared memory on construction and destruction
structshm_remove{shm_remove(){shared_memory_object::remove("MySharedMemory");}~shm_remove(){shared_memory_object::remove("MySharedMemory");}}remover;//Create a new segment with given name and size
managed_shared_memorysegment(create_only,"MySharedMemory",65536);//Initialize shared memory STL-compatible allocator
constShmemAllocatoralloc_inst(segment.get_segment_manager());//Construct a vector named "MyVector" in shared memory with argument alloc_inst
MyVector*myvector=segment.construct<MyVector>("MyVector")(alloc_inst);for(inti=0;i<100;++i)//Insert data in the vector
myvector->push_back(i);//Launch child process
std::strings(argv[0]);s+=" child ";if(0!=std::system(s.c_str()))return1;//Check child has destroyed the vector
if(segment.find<MyVector>("MyVector").first)return1;}else{//Child process
//Open the managed segment
managed_shared_memorysegment(open_only,"MySharedMemory");//Find the vector using the c-string name
MyVector*myvector=segment.find<MyVector>("MyVector").first;//Use vector in reverse order
std::sort(myvector->rbegin(),myvector->rend());//When done, destroy the vector from the segment
segment.destroy<MyVector>("MyVector");}return0;};

The parent process will create an special shared memory class that allows
easy construction of many complex data structures associated with a name.
The parent process executes the same program with an additional argument
so the child process opens the shared memory and uses the vector and erases
it.

Just like a vector, Boost.Interprocess allows
creating maps in shared memory and memory mapped files. The only difference
is that like standard associative containers, Boost.Interprocess's
map needs also the comparison functor when an allocator is passed in the
constructor:

#include<boost/interprocess/managed_shared_memory.hpp>#include<boost/interprocess/containers/map.hpp>#include<boost/interprocess/allocators/allocator.hpp>#include<functional>#include<utility>intmain(){usingnamespaceboost::interprocess;//Remove shared memory on construction and destruction
structshm_remove{shm_remove(){shared_memory_object::remove("MySharedMemory");}~shm_remove(){shared_memory_object::remove("MySharedMemory");}}remover;//Shared memory front-end that is able to construct objects
//associated with a c-string. Erase previous shared memory with the name
//to be used and create the memory segment at the specified address and initialize resources
managed_shared_memorysegment(create_only,"MySharedMemory"//segment name
,65536);//segment size in bytes
//Note that map<Key, MappedType>'s value_type is std::pair<const Key, MappedType>,
//so the allocator must allocate that pair.
typedefintKeyType;typedeffloatMappedType;typedefstd::pair<constint,float>ValueType;//Alias an STL compatible allocator of for the map.
//This allocator will allow to place containers
//in managed shared memory segments
typedefallocator<ValueType,managed_shared_memory::segment_manager>ShmemAllocator;//Alias a map of ints that uses the previous STL-like allocator.
//Note that the third parameter argument is the ordering function
//of the map, just like with std::map, used to compare the keys.
typedefmap<KeyType,MappedType,std::less<KeyType>,ShmemAllocator>MyMap;//Initialize the shared memory STL-compatible allocator
ShmemAllocatoralloc_inst(segment.get_segment_manager());//Construct a shared memory map.
//Note that the first parameter is the comparison function,
//and the second one the allocator.
//This the same signature as std::map's constructor taking an allocator
MyMap*mymap=segment.construct<MyMap>("MyMap")//object name
(std::less<int>()//first ctor parameter
,alloc_inst);//second ctor parameter
//Insert data in the map
for(inti=0;i<100;++i){mymap->insert(std::pair<constint,float>(i,(float)i));}return0;}